1. Field of Invention
The present invention relates to a liquid crystal device, and more particularly to a liquid crystal device that utilizes a transverse electric field. The invention also relates to a projection type display system and electronic equipment using the liquid crystal device.
2. Description of Related Art
Liquid crystal display systems have long been the subject of increasing demand as not only a direct-vision type, but also a projection type display element of an apparatus, such as a projection television. When using the liquid crystal display system as the projection type system, an increase in magnification with a previous pixel number causes image roughness to become remarkable. Thus, in order to obtain a fine image even with a high magnification, it becomes necessary to increase the pixel number. However, an increase in the pixel number of the liquid crystal display system, in particular in an active matrix type liquid crystal display system, relatively increases an area occupied by a portion other than that of the pixel, for example, a portion of an interconnection or a thin film transistor (active element). This causes an increase in an area of a black matrix covering the above portion to reduce a pixel opening area contributing to the display, which causes a problem of reducing an aperture ratio as a display system.
The reduction in the aperture ratio darkens the image to degrade an image grade as a liquid crystal display system.
Thus, in order to reduce or prevent the reduction in the aperture ratio as much as possible due to such an increase in the pixel number, in some of the projection type display systems, a transmission type liquid crystal panel is being shifted to a reflection type liquid crystal panel. By providing the liquid crystal panel as a reflection type, it becomes possible to form interconnection portions, such as scanning lines and signal lines, under a reflection electrode to allow an aperture ratio of a pixel to be increased.
However, even with advent of such various kinds of projection type display systems, in a high resolution liquid crystal panel, a distance between pixels, that is, a distance between pixel electrodes, becomes small. Thus, the high resolution liquid crystal panel has a problem in that an a pixel is affected by a transverse electric field from peripheries of other adjacent pixel electrodes, which causes disclination of the liquid crystal to produce defects in a display region. A detailed explanation of the defects in the display region is provided below.
In a current liquid crystal panel for a projector with a highly fine structure, a rectangular pixel electrode is finely prepared with a width of the order of 20 μm. A plurality of such pixel electrodes are arranged in matrix-like in the display region. In a liquid crystal panel with such a highly fine structure to which a reflection type structure is employed, a structure is employed in which switching elements formed on a substrate are covered with an insulation layer on which pixel electrodes are arranged without producing any gap. This enables a distance between pixel electrodes to be narrowed down to 1 μm or less.
In a highly fine liquid crystal panel having a structure with an interelectrode space of the pixel electrode thus narrowed, a strong transverse electric field will act on a liquid crystal that exists at a boundary portion between adjacent pixel electrodes. The liquid crystal, which is originally to be controlled between a common electrode and pixel electrodes formed on respective inner surfaces of opposing substrates, is affected by the transverse electric field to have a high possibility of being orientated in a different direction. Namely, in the liquid crystal in a region where the orientation of the liquid crystal is to be controlled by the pixel electrode, a part of liquid crystal is made to be directed in directions that are subtly different from those of the other liquid crystal. This causes a problem of producing linear display defects, called disclination lines, at a boundary region with the liquid crystals with the orientating directions being subtly different. An actual measurement of widths of the linear display defects in such a kind of liquid crystal display system has revealed that the width is of the order of about 3 μm in average.
The problem of the display defects due to such a transverse electric field occurs not only in the projection type display system, but also in a highly fine direct-vision type liquid crystal device.
With an object of eliminating such display defects, liquid crystal devices were studied which are proposed in claim 50 to claim 65 in Japanese Patent Laid-Open No. 202356/1999. A related art liquid crystal device is disclosed wherein the liquid crystal is controlled by a so-called longitudinal electric field produced between a pixel electrode and a common electrode, respectively formed on inner faces of a pair of substrates. Compared with this, in each of the proposed liquid crystal devices, a transverse electric field, produced when a space between the pixels becomes narrow, is positively utilized with an intention of realizing a liquid crystal system without display defect. However, the liquid crystal devices proposed in Japanese Patent Laid-Open No. 202356/1999 relate to transmission type liquid crystal devices, whose respective conditions and structures can only be applied to a transmission type liquid crystal device.